Follow-up pressure fluid servomotor



Aug. 8, 1950 E. sALL 2,517,718

FOLLOW-UP PRESSURE FLUID sERvoMoToR Filed April 24, 194s ERM SLL Patented Aug. 8, 1950 FoLLowUP PRESSURE FLUm sERvoMo'roR Erik Sll, Stockholm, Sweden, assigner to Aktiebolaget A. Ekstrms Maskinaffr, Stockholm, Sweden, a joint-stock company` of Sweden Application Apriizi, 1946, Serin No. 664,479 In Sweden November 30,1943

For automatic adjustment of valves, rheostats 5 claims. (o1. lso-52) orthelike for control of liquids, gases, temperal tures, electric currents andsoon a return device is in many cases necessary, in order to `avoid the controlmember (valve or the like) being adjusted *more than necessary and to return the control-aggregate to the position of equilibrium (the initial position). cases'where a certain time elapses from the adjustment of the control member and until the change of this adjustment `has made itself felt inthe memberfreceiving theimpulses ofthe var-- iations (the impulse member) it is of importance that the control member is not adjusted more than necessary for restoring the equilibrium in the control procedure in order to avoid overcontrol` and oscillation.

Thepresent invention relates to such control device with gentle return and with an impulse member independent thereof, which impulse i Particularly in those member by means of gas or liquid pressure actuates a relay in one direction, which relayactuates a servo-motor device consisting e. g. of a pressure cylinder with piston, reversible motor, membrane or the"` like for actuation* of `control means, which control means is substantially characterized therein that the relay which consists of an air dome provided with aiiloat and at least one open return chamber communicating with the said dome, is adaptedto be actuated by a liquid uid in the ldirection oppositeto said gas or liquid pressure, which fluid is actuated by and obtains its movement from the servo-motor device,'the'return chamber communicating with a vessel with means for keeping a substantially constant liquid level therein.

Anembodiment selected as example of a consleeve 6 which is formed in one of the axle journalsof the pump and thus rotates, and a round slide 'I consisting of two piston I parts 8 connected with a narrow intermediate portion. As the slide 1, 8 is arrangedin a rotating sleeve 6, the friction resistance is reduced at the displacement` of the slide. An annular channel 9 in the l valve `casing and apertures I0 in the rotatable sleeve communicate with the pumpthrough the;

pipe line 4. Another annular channel 2l in the valve casing and apertures 22 in the rotating" '1 sleeve communicate with an oil outlet pipe 23.`

An annular channel II in the valve casing and apertures I2 in the rotatable sleeve communi` catewith a servo-motor through a pipe line I3,M said servo-motor consisting in the embodiment 1 shown of a pressure cylinder I4 with a piston I5 connected with a rod I6 which by means of a wire II is connected with the control member, in this case `a control valve I9 which is loaded by a counterweight 2B. 24' is a spring-loaded overnow valve mounted in the pressure pipe of the pump for setting the desired pressure therein.

The surplus of thepumped-up oil, i. e. of the oil not owing into the pressure cylinder I4, flows "1 through a pipe line 25 to a constant level vessel 26.. 21 is a fan which presses air through a pipe Said pipe line is provided with a con-` stricted portion 29 which is preferably dimena soned in such a way that the air pressure in the I pipe line becomes about half as high as before 1 the same. The outliow of the air from the pipe line at the outflow nozzle 30a, is more or less .l checked by a valve 3l! which is actuated by a thermostat 3| mounted in a vessel 32 in which the temperature is to be controlled. Cold liq- I f line 28.

uidis supplied to the vessel through a pipe line 33 and hot liquid through a pipe line controlled by the control Valve I9. The pipe line 28 communicates with an air dome 35 in an intermediate relay, which in this example, besides the air the air dome; slide 'I `by meansof the rod 39 and an angle arm 40 pivoted at 4I. A counterweight 42 maintains the equilibrium of the float. The return chamber 3'!" and the air dome 35 communicate with one another and with the constant level vessel I Y The chamber 43 below the piston in the cylinder I4 is lled` 26 through'the throttle valve' I8.

with a non-compressible liquid and communicates with the returnchamber and the air dome through the return pipe line 44.

The described device operates in the following manner:

When the slide T assumes the position shown in the drawing the apertures Il) and 22 in the rotatable sleeve are shut off by the piston portions 8 of theslide. The valve assumes this position when the temperature in the vessel 32 is normallthe desired temperature).l The oil i sucked by the pump through the pipe 3 from the oil store in the casing I and fed to the pipe line 4 thus cannot pass through the slide 'l and the apertures IU, but leaves through the overflow valve 24 which opens at a certain pressure limit so that the oil leaves, through the pipe line 25 to the constant level vessel 26, from where it oWs down into the oil tank as indicated by the arrows 26a. Nor Ican the oil in the cylinder I4 leave through the sleeve and the slide, and therefore the apparatus has a stable position, i. e. position of equilibrium. The level in the return chamber 31 is then the same as in the oompartment 26.

If the temperature at the thermostat 3l in the vessel 32 rises, the outiiow nozzler 30a, is choked to a certain degree by the valve 30 connected with the thermostat, whereby the resistance to outflow of the air from the pipe 28 is increased. The air pressure then rises in the air dome 35, whereby thel level in the air dome and thus also theiioat sinki and the latter displaces the slide 'l by means of the lever transmission. The apertures I0 in the.- rotatable sleeve are now laid free so that oil. ilows into the pressure cylinder i4, the piston I being: displaced downwards some distance, resulting; in the control valve I9 being choked a little so. that the flow of the1 hot liquid to the vesselv 352-. is. reduced whereby the temperature sinks.v

While the` piston |55 is' displaced downwards., oil iiowsl from the cylinder chamber 43 through the linelll:y to the return'` chamber 3l, although chambers. 3l and 26 are interconnected, valve I8- throtrles. the'ow from chamber 37 intov overflow chamber 25, whereby the level in chamber 31'!Av rises and. thusv also the level and the iloat in the air dome. so thatt they come tothe normal or equi" libriu-m. position, the slide l' then being also dis- I placed to its position of equilibrium so that the:

apertures Ill inz the rotatable sleeve are closed. If the temperature` in the'vessel 32 continues to. rise, the outilow nozzle 39a is still more` choked bythe thermostat valve 33, thereby raising still more the air pressure in. the air` dome 35 so that the level' therein andthe float sink belowl the po,- sition of equilibrium. This results in thatY the apertures. I-ll are.y opened and more oil flows into the pressure cylinder so thatv the piston therein is pressed still more downwards and the control. valve I9 is further choked. Now still more oil ilows from' the. cylinder chamber 43 to the return chambery 3l, and thev piston continues to move.

downwards until sol much oil has flown into the return, chamber that the level and the fica-t. in thev airdome rise toy the position of equilibrium, the: level in the return chamber rising at the same time so. much that it is. in equilibrium with'the higher air pressure in the air dome. When the control valve i9. has been choked so much that the temperature does not rise further aty the ther-l mostat but is stillv higher than the normal tem-v perature corresponding to a higher air pressure in the air dome, the oil level in the return chamber is thus higher than normally (there` isv equilibrium between this air pressure and the oil column). Although the temperature is stillv too high no oil does thus flow, into the pressure cylin` der. Due to the reduced supply ofr the hotter liquid to the vessel 32 the temperature graduallyA sinks at the thermostat so that the distance is increased between the valve 30 and the outflow nozzle 30a, which results in a continuously re-v duced checkingA of the outow of the air from the pipe line, the pressure in the air dome sinking more" and' more. This continues until. the

temperature is normal again when also the distance between the valve and the outliow nozzle is normal again. Meanwhile oil has flown out from the return chamber through the choke valve I8 to the constant level vessel so that the levels in the return chamber and in the said vessel will be in. equilibrium.. 1

The return speed is set by the choke valve I8 and is suited to the working conditions. Its position is correct when the level in the return chamber and the air pressure in the pipe line 28, and the air'dome respectively, at the same time are in equilibrium after the control device has been in function.

When the temperature in the vessel 32 sinks under the normal value the same procedure is repeated', although in the opposite direction. The pressure in the pipe line 28 then sinks under the normal value, so that the float rises and displaccs the slide l to the left, oil then flowing out from the pressure cylinder through the apertures 22` and the pipeline 23, the piston I5 being displaced' upwards and the oil level, in the return chamber` sinking. The above described embodiment is onlyJ citedf.

by way of example. Thus, other devices; may be;

used as servo-motors, e. g. a reversible electric.

motor, the relay actuating electric contacts of said motor. In this case the liquid for the-*why-l draulic return movement may be actuated by a piston, membrane or the like which is connected. with e. g. a lever for the control member |901 some member for motion transmission from thef servo-motor to the control member.

when an electric current is to be controlled;

Pressure fluidv forv pressure cylinders' mem.-

branes andso on may be taken from anotherpressureisource thana pump. Instead; of the shown slide; valve another valve or some other member may bel used.

The. liquid in the return chamber may also. be

actuated indirectly by a separate cylinder, mem.-

brane or-the like connected with the; servo-motor',

the control member I9V or some member transmit'-V ting the movement. between the servo-motor and control member.

Aniston, membrane, bellows or the. like may be l' used in the relay instead of Iioat'. Some other".

liquid may be used instead of oil.

Diierent impulse members are used acoordingiv to .the objects to beoontrollede. g.. electromaig`L` net, Bourdon tube, oatpimpulse member for;

respects in comparison with what has been. dee scribed above and disclosed on the drawing' with;l out going beyond the scope of the invention..

Having nowy described` my invention, what; In" claim as new and desire to secure by letters'.

Patent is:

l. A control device with a gentle return. and with an impulseA member independent thereof,

comprising a relay, the said impulse member' by' means of iluid pressurer actuating the relayv in one direction, control means, thel relay actif-i' ating a servo-motor device for regulation ofthe control means, the said relay consisting" of an" air dome provided with a iioat and at least Orieopen return chamber communicating with thev said dome, the said relay being furthermore? adapted to be actuated by a liquid fluid in the direction opposite to said uid pressure which iiuid is actua-ted by and obtains its movement-F from the servomotor device, the return chamber communicating via an adjustable throttle valve With a- Vessel With means for keeping a substantially constant liquid level therein.

2. A device as claimed in claim 1 said servo motor device consisting of a pressure cylinder with "piston and a pump connected therewith via a valve device, an automatic overiow valve, the pressure pipe of the pump being connected with the constant level vessel via the automatic overflow valve.

3. A device as claimed in claim 2, in Which the return chamber communicates with the pressure cylinder.

4. A device as claimed in claim 1, a rod controlling the servo-motor device and connected with the float, said rod passing through a pipe passing through the return chamber and extending above its liquid level, a second pipe displaceably located around the rod and the float, said 20 second pipe being closed at the top and open at 6 the bottom beneath the level of the liquid uid in the air dome.

5. A device as claimed in claim l, including a motor-driven rotatable sleeve, a second slide displaceably mounted in said sleeve, said rela-y actuating the said servo-motor by means of said second slide, and an outer casing in which said sleeve is located, said sleeve being provided With apertures corresponding to liquid passages in said slide and in said casing.

ERIK SLL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,012,978 Veenschoten Sept. 3, 1935 2,117,891 Kalin May 17, 19,38 2,320,508 Burns June 1, 1943 

